Butanol is an important industrial chemical with a variety of applications, including use as a fuel additive, as a feedstock chemical in the plastics industry, and as a food-grade extractant in the food and flavor industry. Accordingly, there is a high demand for butanol, as well as for efficient and environmentally friendly production methods. One such environmentally friendly production method includes the production of butanol utilizing fermentation by microorganisms. During the fermentation process, butanol can be extracted from the fermentation medium using an extractant.
The use of fatty acids as an extractant for recovering butanol from a fermentation process is attractive as fresh fatty acid can be constantly generated by lipase-catalyzed hydrolysis of available corn oil, introduced with the corn mash. The ratio of linoleic:oleic:palmitic acid in corn oil triglycerides is approximately 4:2:1 on a weight basis. Given the high concentration of polyunsaturated fatty acids, the risk of oxidation is high if the polyunsaturated fatty acids are allowed contact with oxygen, which may occur during fermentation and/or during other steps of the process for producing butanol. Antioxidants, particularly the tocopherols, associated with raw corn oil provide some protection. However, given that the fatty acids generated from the corn oil can be reused and recycled to extract fermentative products such as butanol many times and the fact that the antioxidant is consumed when it interrupts the oxidation cycle, a sufficient amount of antioxidants or antioxidant-like compounds in the extractant is needed to keep the rate of oxidation at an acceptably low level or to counteract the effect of oxidation products (e.g., aldehydes and ketones), particularly when the fermentation process is carried out under aerobic and/or microaerobic conditions.
The present invention satisfies the need to maintain or provide an effective level of antioxidants or antioxidant-like compounds in an extractant for recovering butanol from a fermentation process.